Former US president in politics?

With my limited knowledge of US politics, I can’t think of any US presidents who, after their term is over, took another political office like senator or governor. What are some examples I should know about (if any), and why is it rare?

Taft was appointed Chief Justice after his presidency.
John Quincy Adams served in the House of Representatives after his presidency.

Oh, and as to why it’s rare, these days the President of the United States is the most powerful person on the planet. Going from the position of being the most powerful person on the planet to one of 100 senators or one of 50 governors or one of 435 representatives, or even worse, running for one of those positions and losing, would be a fairly ignominious end to an amazingly successful political career.

Didn’t we just do this thread like a week ago?

Another reason it’s rare is that most ex-presidents are up there in age after their term.

Another reason might be that being President takes an enormous toll on them physically. Most presidents seem to have aged way more than the four or eight years they were in office.

If I were that worn out, I’d probably just as soon retire as well.

Plus, why do anything but kick back enjoying the perks that come with being an ex-president?

And, yes, we DID just do this a couple weeks ago:

http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=225595

Ah thanks, and my apologies for not doing a search properly.